Yemeni tribesmen attacked an army camp near the capital Sanaa on Thursday sparking clashes in which dozens on both sides were killed or wounded, the military and tribesmen said.
"Armed groups of hundreds" attacked an army post in Samaa, 40 kilometres (25 miles) northeast of Sanaa, the defence ministry news website, 26sep.net, quoted a military official as saying.
A group of "criminal elements" infiltrated the camp while another group "shelled it, using various weapons," killing or wounding several soldiers, said the official.
The army responded "and both sides clashed fiercely ... bringing massive losses" upon the attackers, said the official.
Tribal sources confirmed casualties, saying that "dozens were killed and wounded" from both sides.
The army called in air support against the tribesmen who took over part of a camp held by Republican Guard troops, loyal to embattled President Ali Abdullah Saleh, the tribal sources said.
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No specific tolls were immediately available.
Deputy Information Minister Abdo al-Janadi accused Mansur al-Hanaq, a former member of the influential opposition Islamist Al-Islah (Reform) party, of being behind the attack.
The military official said "these armed criminal elements aimed to control the Samaa camp in an attempt to take over Sanaa International airport as part of their plan to overthrow the constitutional legitimacy and seize power by force," 26sep.net said.
Meanwhile, in the flashpoint city of Taez, south of Sanaa, a brief ceasefire between pro-opposition armed tribesmen and the police collapsed and clashes resumed on Thursday.
Witnesses said tribesmen shot dead one policeman and wounded another.
Tribesmen, who say their aim is to protect protesters who demand Saleh stand down, have battled security forces loyal to Saleh in Taez since June.
Saleh, who has been in power since 1978, has been receiving treatment in Saudi Arabia since early June for wounds sustained in a blast at his palace.